The mcast directive is used to configure a multicast communication path.
The syntax of an mcast directive is:
mcast dev mcast-group udp-port ttl 0
dev - IP device to send/rcv heartbeats on
ttl - the ttl value for outbound heartbeats. This affects how far the multicast packet will propagate. (0-255). Set to 1 for the current subnet. Must be greater than zero.
A sample mcast directive is shown below:
mcast eth0 188.8.131.52 694 1 0
This directive has a few more parameters than it should.